Igneous Geochronology and Thermochronology of the Northern Battle Mountain District, Nevada: Implications for Gold Mineralization

The Battle Mountain mining district of north-central Nevada hosts a variety of gold deposit types, including Cu-Au porphyries and skarns, polymetallic veins, and sedimentary rock-hosted disseminated Au deposits. This study examines intrusions in the northern part of the district, with a focus on those spatially associated with the sedimentary rock-hosted disseminated Au deposits. We identify three periods of magmatism in the district using zircon U-Pb geochronology-Jurassic (similar to 162 Ma), Cretaceous (similar to 97-92 Ma), and Eocene (similar to 40-39 Ma)-which we attribute to magma periodically exploiting a structural fabric that developed over a Late Proterozoic rift structure. New district-scale geophysical surveys support this process; aeromagnetic data reveal large positive anomalies that we interpret to represent batholiths that grew through repeated injections of magma during the Cretaceous and Eocene. Sedimentary rock-hosted Au deposits are generally located at the margins of these anomalies, suggesting that mineralizing fluids utilized the fracture networks that developed where the rheologic contrast between igneous stocks and the surrounding country rock is most pronounced. Apatite and zircon (U-Th)/He thermochronology identifies district-wide cooling during the Eocene, even at deposits that lack causative Eocene intrusions. We interpret this Eocene date population to represent heating and subsequent cooling from widespread hydrothermal fluid flow, as the (U-Th)/He dates overlap with the formation of Eocene magmatic-hydrothermal Au deposits elsewhere in the Battle Mountain district (e.g., Converse, Buffalo Valley, Elder Creek, Copper Basin, Copper Canyon) and predate rapid exhumation. Time-temperature thermal models on (U-Th)/He aliquots and an absence of alteration zonation constrain fluid temperatures to <210 degrees C during this period. Based on the spatial association with inferred large batholiths at depth and the fluid temperature constrained by thermal modeling, we interpret that Eocene magmatism contributed fluids and heat (and possibly metals) to the sedimentary rock-hosted disseminated Au deposits in the northern Battle Mountain district.